1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention provides luminal prostheses, such as vascular stents and grafts, which allow for controlled substance delivery for inhibiting restenosis in a blood vessel following balloon angioplasty or other interventional treatments.
A number of percutaneous intravascular procedures have been developed for treating stenotic atherosclerotic regions of a patient's vasculature to restore adequate blood flow. The most successful of these treatments is percutaneous transluminal angioplasty (PTA). In PTA, a catheter, having an expansible distal end usually in the form of an inflatable balloon, is positioned in the blood vessel at the stenotic site. The expansible end is expanded to dilate the vessel to restore adequate blood flow beyond the diseased region. Other procedures for opening stenotic regions include directional arthrectomy, rotational arthrectomy, laser angioplasty, stenting, and the like. While these procedures have gained wide acceptance (either alone or in combination, particularly PTA in combination with stenting), they continue to suffer from significant disadvantages. A particularly common disadvantage with PTA and other known procedures for opening stenotic regions is the frequent occurrence of restenosis.
Restenosis refers to the re-narrowing of an artery after an initially successful angioplasty. Restenosis afflicts approximately up to 50% of all angioplasty patients and is the result of injury to the blood vessel wall during the lumen opening angioplasty procedure. In some patients, the injury initiates a repair response that is characterized by smooth muscle cell proliferation referred to as “hyperplasia” in the region traumatized by the angioplasty. This proliferation of smooth muscle cells re-narrows the lumen that was opened by the angioplasty within a few weeks to a few months, thereby necessitating a repeat PTA or other procedure to alleviate the restenosis.
A number of strategies have been proposed to treat hyperplasia and reduce restenosis. Previously proposed strategies include prolonged balloon inflation during angioplasty, treatment of the blood vessel with a heated balloon, treatment of the blood vessel with radiation following angioplasty, stenting of the region, and other procedures. While these proposals have enjoyed varying levels of success, no one of these procedures is proven to be entirely successful in completely avoiding all occurrences of restenosis and hyperplasia.
As an alternative or adjunctive to the above mentioned therapies, the administration of therapeutic agents following PTA for the inhibition of restenosis has also been proposed. Therapeutic treatments usually entail pushing or releasing a drug through a catheter or from a stent. Of particular interest herein, stents may incorporate a biodegradable or nondegradable matrix to provide programmed or controlled release of therapeutic agents within a blood vessel. Biodegradable or bioerodible matrix materials employed for controlled release of drugs may include poly-1-lactic acid/poly-e-caprolactone copolymer, polyanhydrides, polyorthoesters, polycaprolactone, poly vinly acetate, polyhydroxybutyrate/polyhyroxyvalerate copolymer, polyglycolic acid, polyactic/polyglycolic acid copolymers and other aliphatic polyesters, among a wide variety of polymeric substrates employed for this purpose.
While holding great promise, the delivery of therapeutic agents for the inhibition of restenosis has not been entirely successful. In particular, the release of drugs from stents has often been characterized by inconsistent and/or ineffective results because therapeutic agents are often released before they are needed, i.e., before hyperplasia and endothelialization begin. Drug delivery before any cellular or endothelial formation may also pose serious dangers, especially when dealing with the delivery of certain toxic agents. Furthermore, a rapid initial release of drugs causes delayed endothelialization and/or enlargement of the vessel wall, as a substantial number of cells are killed with increased drug loading. The use of drug release matrices can ameliorate the rapid release problems but do not provide programmed time-delay to impact restenosis at the onset of hyperplasia.
For these reasons, it would be desirable to provide improved devices and methods for reducing and/or inhibiting restenosis and hyperplasia following angioplasty and other interventional treatments. In particular, it would be desirable to provide improved devices and methods, utilizing luminal prostheses, such as vascular stents and grafts, which provide programmed and controlled substance delivery with increased efficacy to inhibit restenosis. It would further be desirable to provide such devices and methods which would reduce and/or further eliminate drug washout and potentially provide minimal to no hindrance to endothelialization of the vessel wall. At least some of these objectives will be met by the devices and methods of the present invention described hereinafter.
2. Description of the Background Art
U.S. Pat. No. 5,283,257, suggests that a stent could be used to deliver mycophenolic acid to a blood vessel. Mycophenolic acid methods of production and uses, some of which are intravascular, are described in U.S. Pat. Nos. 6,107,052; 5,916,585; 5,807,876; 5,646,160; 5,563,146; 5,516,781; 4,786,637; 4,753,935; 4,727,069; 4,686,234; 4,234,684; 4,115,197; 3,903,071; 3,880,995; 3,868,454; 3,777,020; 3,705,946; and 3,705,894. Inhibitory effects of mycophenolic acid on human and rat aortic smooth muscle and endothelial cell proliferation is described in Mohacsi et al., J Heart and Lung Trasplant, 16, pp. 484-491 (1997). Animal models of accelerated arteriosclerosis have demonstrated that MPA could decrease the extent of smooth muscle cell proliferation in Gregory et al., Transplant Proc., 25, pp. 770 (1993). A European clinical study reported reduced incidence of acute rejection of patients undergoing kidney transplantation in the first six months after being treated with mycophenolic mofetil in Lancet, pp. 345, 1321 (1995).
Method and apparatus for releasing active substances from implantable and other devices are described in U.S. Pat. Nos. 6,096,070; 5,824,049; 5,624,411; 5,609,629; 5,569,463; 5,447,724; and 5,464,650. The use of stents for drug delivery within the vasculature are described in PCT Publication No. WO 01/01957 and U.S. Pat. Nos. 6,099,561; 6,071,305; 6,063,101; 5,997,468; 5,980,551; 5,980,566; 5,972,027; 5,968,092; 5,951,586; 5,893,840; 5,891,108; 5,851,231; 5,843,172; 5,837,008; 5,769,883; 5,735,811; 5,700,286; 5,679,400; 5,649,977; 5,637,113; 5,591,227; 5,551,954; 5,545,208; 5,500,013; 5,464,450; 5,419,760; 5,411,550; 5,342,348; 5,286,254; and 5,163,952. Biodegradable materials are described in U.S. Pat. Nos. 6,051,276; 5,879,808; 5,876,452; 5,656,297; 5,543,158; 5,484,584; 5,176,907; 4,894,231; 4,897,268; 4,883,666; 4,832,686; and 3,976,071. The use of hydrocylosiloxane as a rate limiting barrier is described in U.S. Pat. No. 5,463,010. Methods for coating of stents is described in U.S. Pat. No. 5,356,433. Coatings to enhance biocompatibility of implantable devices are described in U.S. Pat. Nos. 5,463,010; 5,112,457; and 5,067,491.
The disclosure of this application is related to the disclosures of the following applications being filed on the same day: Ser. No. 09/783,253 Ser. No. 09/783,254 and Ser. No. 09/782,804.
The full disclosures of each of the above references are incorporated herein by reference.